If you make a film, and there seems to be a clear plot hole based ONLY upon the movies, then I do not care about whether a book explains it or not. The movies must stand on their own. Then it closes enjoyment of the film to a smaller subset of people willing to read a book.
The books should purely be new stories entirely or extra content for fun. It cannot serve the role of filling in things that a film failed to do well. If the film failed to do it well, then it is inexcusable for the movies part. And of course, I am speaking generally about any sort of adaptation, entry in a film series, a sci fi world, etc.